Re: use of exceptions in GCC

["lhmouse"<lh_mouse at 126 dot com>]

> GCC is built with -fno-exceptions.  I assume that's mainly to avoid
> having to catch and handle exceptions in what was originally C code.
> I also assume that also means that there's a policy or convention in
> place against throwing exceptions in GCC or making use of constructs
> that might throw (such as the non-placement new expressions).
It also drops the need of _runtime type info_ (a.k.a. RTTI) and stack unwind
table, reducing the size of binary files.

> 
> By coincidence, bootstrapping my patch for bugs 77531 and 78284
> exposed a few uses of the non-placement array new expression in
> dominance.c (in dom_info::dom_init) that may throw an exception(*).
> 
> I'm wondering if those calls should be changed to avoid exceptions.
If a program is compiled with `-fno-exceptions` and an exception
will have been thrown otherwise, `std::abort()` (or an equivalent such as
`__builtin_trap()`) is called. This preserves the semantical correctness
of not checking the value of a throwing new expression,
since it can't return a null pointer.

> 
> I'm also curious if there really is a policy/convention for dealing
> with exceptions in GCC, what it actually is/says.
Compilers aren't envisioned to be long-running programs, so aborting
on unexpected conditions is reasonable. This isn't only the case for GCC,
but also LLVM.

> 
> Thanks
> Martin
> 
> [*] My patch exposed these because when -fno-exceptions is used
> (and coincidentally also in C++ 98 mode) GCC emits conditional calls
> to operator new[](SIZE_MAX) when the size computation that multiplies
> the number of elements by the element size exceeds SIZE_MAX.  The
> -Walloc-size-larger-than warning flags for attempting to allocate
> more storage than the size of the biggest object, or SIZE_MAX / 2.



------------------				 
Best regards,
lh_mouse
2016-11-17